Transfer molding apparatus and method for manufacturing semiconductor device

ABSTRACT

A transfer molding apparatus, wherein said top-half mold and said bottom-half mold form a plurality of cavities interconnected, and wherein said pressure adjusting means reduces the pressure of the cavities every time a specified amount of resin is supplied into any one of a plurality of cavities.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation application of application Ser. No. 10/890,222,filed Jul. 14, 2004, which is a continuation application of applicationSer. No. 09/893,455, filed Jun. 29, 2001, now U.S. Pat. No. 6,767,484,which is a divisional application of Ser. No. 09/265,841 filed Mar. 10,1999, now U.S. Pat. No. 6,267,577, which are hereby incorporated byreference in their entirety for all purposes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a transfer molding apparatus and amethod of manufacturing semiconductor devices.

2. Related Art

In the manufacture of semiconductor devices, transfer moldingapparatuses for encapsulating semiconductor devices mounted on leadframes are conventionally used. As shown in FIG. 7, the transfer moldingapparatus comprises a transfer pot 10 into which solid thermosettingresin (tablets) is loaded, a plunger 12 for transferring thethermosetting resin 28 (hereafter referred to as the resin 28. See FIGS.8(a)-8(d)) that has been fluidified in the transfer pot, a positionsensor 14 for detecting the position of the plunger 12, a top-half mold16 a fixed to a top platen 26 a, a bottom-half mold 16 b fixed to abottom-half platen 26 b, heaters 18 for heating the top-half andbottom-half molds 16 a, 16 b to a predetermined temperature, and asuction pump 24 for reducing the pressure in the cavities 20 byextracting the air from a chamber 30 where the top-half and bottom-halfmolds 16 a, 16 b are disposed.

When the top-half and bottom-half molds 16 a, 16 b are closed, twocavities 20 each for setting up a molding space for a plastic ICpackage, and runners 22 and gates 23 as resin supply paths leading tothe cavities 20 are formed.

When the top-half and bottom-half molds 16 a, 16 b are closed, air-ventslots 25 are also formed at the outer end positions of the two cavities20 opposite the gates 23 located at the inner ends thereof. When thechamber 30 is placed at reduced pressure by extracting air by a suctionpump 24, the air is sucked out from the runners 22 and the gates 23through the air-vent slots 25, so that the cavities 20 are placed atreduced pressure. The runners 22 guide the resin 28 into the cavities 20through the gates 23 that are open to the corresponding cavities 20.

Referring to FIGS. 8(a)-8(d), description will be made of a method ofmanufacturing semiconductor devices on a transfer molding apparatusstructured as described above. FIGS. 8(a)-8(d) show only the principalportions for convenience of explanation. First of all, asemiconductor-device-mounted lead frame (not shown) is set in thebottom-half mold 16 b, a resin tablet is loaded in the transfer pot 10,and by lowering the top platen 26 a, the top-half mold 16 a and thebottom-half mold 16 b are closed, so that a cavity 20, for example, isformed as shown in FIG. 8(a). At this point in time, the semiconductordevice has been placed almost in the center of the cavity 20. Inaddition, the pressure in the chamber 30 has been reduced to about 30 to99 Pa by the suction pump 24.

While the resin tablet charged in the transfer pot 10 is being melted byheating it to 160° to 190° C. with the heaters 18, the resin is extrudedfrom the transfer pot 10 by raising the plunger 12. By this operation,the molten resin 28 is introduced into the runner 22 as shown in FIG.8(b).

By the increasing the forcing pressure from the plunger 12, the resin 28in the runner 22 is guided through the gate 23 into the cavity 20 asshown in FIG. 8(c). As shown in FIG. 8(d), when the resin 28 has beenfilled into the cavity 20, the forcing pressure from the plunger 12 isstopped, and the resin 28 in the cavity 20, the runner 22, and the gate23 is cured. After the resin 28 is cured sufficiently, the top platen 26a (see FIG. 7) is raised, and the semiconductor device with a lead framein a package of resin 20 that hardened around the semiconductor elementis ejected. Subsequently, the excess resin is removed and whittled downto shape, and the lead-frame portion is cut off and the outer leads areformed to thereby produce a semiconductor package. Subsequently, theexcess resin is removed, the package is whittled down to shape, theframe portion of the lead frame is trimmed, and the outer leads areformed. Thus, a semiconductor device is produced.

In the transfer molding apparatus constructed as described, there arepossibilities of an unfilled region (voids) 29 being formed in thetop-cavity portion or the bottom-cavity portion of the mold due to adifference in resin-filling speed between the top-cavity portion and thebottom-cavity portion, which partition is made by the semiconductorelement loaded in the cavity 20. Voids are unwanted because they giverise to a warp or deformation in the package or decreases its strengthor humidity resistance.

There have been countermeasures against the voids. One is to provide asuction port communicating with the cavity, and directly reduce thepressure in the cavity by the use of a suction pump to decrease theremaining air in the top-cavity portion or the bottom-cavity portion toprevent the occurrence of voids. The other is to place the chamber 30itself in a reduced-pressure atmosphere so that the remaining air in thetop-cavity portion or the bottom-cavity portion should be extractedthrough the air-vent slot 25 and to thereby prevent the occurrence ofvoids.

However, in the transfer molding apparatus constructed as describedabove, because the resin passes through the gate of a smaller diameterthan that of the runner when it enters a cavity, the resin is subjectedto pressure at the gate, and the resin in compressed state is injectedinto the cavity. Therefore, if the cavity is at reduced pressure when aspecified amount of resin is introduced into the cavity, there is arelatively large pressure difference between the pressure in the cavityand the pressure in the resin. A problem here is that when there is sucha large pressure difference, the air bubbles in the resin expandnotably, and remain as voids in the package.

Thermosetting resins have a characteristic that curing does not progressin proportion to the passage of time, but curing occurs after theviscosity decreases once. Therefore, with some kinds of thermosettingresins, the viscosity sometimes drops temporarily while the cavity isbeing filled with a molding compound. Also in this case, there is aproblem that the air bubbles expand remarkably in the resin and remainas voids in the package.

SUMMARY OF THE INVENTION

The present invention has been made to solve the above problems, and hasas its object to provide a transfer molding apparatus and a method formanufacturing semiconductor devices, which are free of voids remainingin a resin when filled in the cavities.

To achieve the above object, the transfer molding apparatus according tothe present invention comprises:

a top-half mold and a bottom-half mold for forming a cavity as a moldingspace for a package and a transfer pot as a loading space, communicatingwith the cavity, for resin to be injected into the cavity;

a plunger for forcing the resin out of the transfer pot into the cavity;and

a pressure adjuster for reducing the pressure in the cavity when aspecified amount of resin has been injected into the cavity.

Because the pressure adjuster reduces the pressure in a cavity after aspecified amount of resin has been injected into the cavity, the cavityis at normal pressure at a point in time when the supply of a specifiedamount of resin is finished and the pressure difference between thepressure in the cavity and the pressure in the resin is relativelysmall. Therefore, the air bubbles in the resin can be prevented fromexpanding remarkably.

Because the pressure adjuster reduces the pressure in a cavity when aspecified amount of resin has been injected into the cavity, theremaining air in the unfilled region of the top cavity portion or thebottom cavity portion can be decreased, so that the voids can bereduced, which occur due to a difference in filling rate between the topcavity portion and the bottom cavity portion.

In the transfer molding apparatus described above, the top-half mold andthe bottom-half mold form a plurality of interconnected cavities, andthe pressure adjuster reduces the pressure of the cavities every timeany one of the plurality of cavities is supplied with a specified amountof resin.

Even in such a construction that a plurality of cavities are connectedto one transfer pot, each cavity is kept at normal pressure until it issupplied with a specified amount of resin. Therefore, the entrapped airin the resin in each cavity when it is filled with the specified amountof resin can be prevented from expanding to a great extent, with theresult that it is possible to efficiently obtain semiconductor devicesin packages of good quality.

Further, in the transfer molding apparatus, the pressure adjuster has aposition detector for detecting the position of the plunger, and reducesthe pressure in each cavity by detecting the plunger position at a pointin time when the cavity has been supplied with a specified amount ofresin. By using this mechanism, the injected amount of resin can bedetected with high accuracy, which makes it possible to suitably controltiming of pressure reduction by the pressure adjuster.

In the transfer molding apparatus described above, the pressure adjusterhas a time counter, and reduces the pressure in a cavity when the timecounter has counted a set length of time from the start of movement ofthe plunger until the cavity is supplied with a specified amount ofresin.

More specifically, a length of time from the start of plunger movementuntil the cavity is supplied with a specified amount of resin ismeasured, and at the end of a preset time, the pressure adjuster reducesthe pressure in the cavity. Therefore, it is possible to detect theinjected amount with high accuracy, and suitably control timing ofpressure reduction by the pressure adjuster.

In the method for manufacturing semiconductor devices, asemiconductor-element-mounted lead frame is placed between the top-halfmold and the bottom-half mold, and the pressure in a cavity is reducedwhen a specified amount of resin has been filled in the cavity formed bythe top-half mold and the bottom-half mold.

In other words, according to, the method according to the presentinvention, because the pressure in a cavity is not reduced until thecavity is supplied with a specified amount of resin, the cavity prior toinjection of resin is maintained at normal pressure. For this reason, apressure difference between the pressure in the resin and the pressurein the cavity is relatively small when the cavity has been supplied withresin. Therefore, the entrapped air in the resin can be prevented fromexpanding remarkably.

Needless to say, because the pressure in the cavity is reduced after thecavity has been supplied with a specified amount of resin, the remainingair in the unfilled region of the top-cavity portion or thebottom-cavity portion can be reduced, and it becomes possible to preventthe occurrence of voids due to a difference in filling rate between thetop-cavity portion and the bottom-cavity portion.

BRIEF DESCRIPTION OF THE DRAWINS

FIG. 1 is a sectional view showing a schematic construction of atransfer molding apparatus according to a first embodiment of thepresent invention;

FIGS. 2(a)-2(d) are fragmentary diagrams for explaining the motion ofthe transfer molding apparatus shown in FIG. 1;

FIG. 3 is a sectional view showing a schematic construction of thetransfer molding apparatus according to a second embodiment of thepresent invention;

FIGS. 4(a)-4(d) are fragmentary diagrams for explaining the motion ofthe transfer molding apparatus shown in FIG. 3;

FIG. 5 is a sectional view showing a schematic construction of thetransfer molding apparatus according to a third embodiment of thepresent invention;

FIGS. 6(a)-6(d) are fragmentary diagrams for explaining the motion ofthe transfer molding apparatus shown in FIG. 5;

FIG. 7 is a sectional view showing a schematic construction of aconventional transfer molding apparatus; and

FIGS. 8(a)-8(d) are fragmentary diagrams for explaining the motion ofthe transfer molding apparatus shown in FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described with reference toFIGS. 1 to 6(a)-6(d).

First Embodiment

A first embodiment will be described with reference to FIGS. 1 and2(a)-2(d). As shown in FIG. 1, the transfer molding apparatus accordingto the first embodiment comprises a top-half mold 16 a fixed to a topplaten 26 a; a bottom-half mold 16 b fixed to a bottom platen 26 b;heaters 18 for heating the top-half and the bottom-half molds 16 a, 16 bto a predetermined temperature; a transfer pot 10, formed by thetop-half and the bottom-half molds, for accepting a tablet of athermosetting resin, an epoxy resin for example, formed by the top-halfand the bottom-half molds 16 a, 16 b; a plunger 12 for extruding theresin 28 melted in the transfer pot 10; a position sensor 14 fordetecting the position of the plunger 12; a suction pump 24 for reducingthe pressure in a chamber 30, having the top-half mold 16 a and thebottom-half mold 16 b installed therein, thereby placing the cavities 20at reduced pressure; and a pressure controller 40 for controlling thedrive of the suction pump 24 according to the amount of movement of theplunger 12.

When the top-half mold 1 a and the bottom-half mold 16 b are closed, twocavities 20 as molding spaces for packages and two runners 22 forguiding the resin into the cavities 20 through gates 23, which are opento the cavities 20, are formed. The runners (distribution paths) 22 areprovided on both sides of the transfer pot 10 and communicate with eachother through the transfer pot 10.

An air-vent slot 25 is formed on the side of each cavity 20 that isopposite the side open to the gate 23. As will be described later, whenthe chamber 30 is placed at reduced pressure by using a suction pump 24,the air in the cavities 20 is extracted through the air-vent slots 25,so that the cavities are also placed at reduced pressure.

The pressure controller 40 drives the suction pump 24 to reduce thepressure in the chamber 30 when the position sensor 14 detects that theplunger 12 is at the position indicating that each cavity has beensupplied with a specified amount of resin. The pressure controller 40causes the suction pump 24 to stop when the position sensor 14 detectsthe position of the plunger 12, which indicates that the cavities 20have been filled with resin 28. Then, the pressure controller 40 bringsthe chamber 30 to normal pressure by releasing a vent valve of thechamber 30.

Referring to FIGS. 2(a)-2(d), description will now be made of a methodfor manufacturing semiconductor devices on the transfer moldingapparatus constructed as stated. Note that FIGS. 2(a)-2(d) show theprincipal parts only for convenience of explanation. Asemiconductor-element-mounted lead frame (not shown) is set in thebottom-half mold 16 b, then a resin tablet is charged in the transferpot 10, and by lowering the top platen 26 a, the top-half mold 16 a andthe bottom-half mold 16 b are closed as shown in FIG. 2(a). At thistime, the semiconductor element, not shown, has been placed almost inthe center of the cavity 20.

Then, while the tablet charged into the transfer pot 10 is melted byheating it to 160° to 190° C., the plunger 12 is raised to extrude theresin from the transfer pot 10. Consequently, the molten resin 28 isintroduced into the runner 22.

The position sensor 14 is detecting the position of the plunger 12 fromthe start of its movement. As shown in FIG. 2(b), the position sensor 14outputs a detection signal to the pressure controller 40 when theposition sensor 14 detects that the leading end of the plunger 12 hasreached the position B, which indicates that a specified amount of resinhas been supplied from the runner 22 into the cavity 20.

On receiving a detection signal from the position sensor 14, thepressure controller 40 transmits a drive start signal to the suctionpump 24. In response to the drive start signal, the suction pump 24starts to extract the air from the chamber 30, and gradually reduces thepressure in the chamber 30 to about 30 to 90 Pa. Therefore, even if theresin 28 has been compressed at position of the gate 23 and thepressurized resin 28 is injected into the cavity 20, because the cavityis gradually changed from normal pressure to reduced pressure, therelative pressure difference between the pressure acting on the airbubbles in the resin 28 and the pressure in the cavity 20 can be limitedto a small degree, the air bubbles entrapped in the resin can beprevented from expanding greatly.

Timing for reducing the pressure in the chamber 30 by using the suctionpump 24 may be when the resin decreases in viscosity and starts toharden, for example (in this case, when the resin 28 has been injectedto about one half of the cavity 20 as shown in FIG. 2(c)). In otherwords, the timing for chamber pressure reduction may be when the leadingend of the plunger 12 has reached the position C.

As described above, if the pressure in the chamber 30 is decreased afterthe viscosity of the resin has decreased, because the resin has startedto harden, the air bubbles in the resin are less liable to expand.

As shown in FIG. 2(d), when the cavity 20 is completely filled withresin 28, in other words, when the leading end of the plunger 12 hasreached the position D, the position sensor 14 outputs a detectionsignal to the pressure controller 40. When receiving the detectionsignal from the position sensor 14, the pressure controller 40 transmitsa drive stop signal to the suction pump 24 to stop its operation. On theother hand, the chamber 30 is brought back to normal pressure. At thesame time, the plunger 12 is stopped. Subsequently, the resin 28 iscured.

After the resin 28 has been sufficiently cured, the top platen 26 a (seeFIG. 1) is raised, and a semiconductor device with a lead frame in apackage of resin 28 that hardened around the semiconductor element isejected. Subsequently, the excess resin remaining in the runner 22 orthe like is removed, the package is whittled down to shape, the frameportion of the lead frame is trimmed, and the outer leads are formed.Thus, a semiconductor device is obtained.

As has been described, in the first embodiment, when the position sensor14 detects that a specified amount of resin 28 has been injected intothe cavity 20, the pressure controller 40 causes the suction pump 24 tooperate to reduce the pressure in the cavity 20. Therefore, the relativepressure difference between the pressure acting on the air bubbles inthe resin 28 and the pressure in the cavity 20 can be limited to a smalldegree until the cavity 20 is supplied with a specified amount of resin28. For this reason, the air bubbles in the resin 28 can be preventedfrom expanding remarkably, which makes it possible to eliminate chancesof voids remaining in the package.

If the pressure in the chamber 30 is reduced after a drop occurred inthe viscosity of the resin 28 being injected into the cavity 20, itfollows that the curing of the resin has started. In this case, the airbubbles in the resin 28 can be prevented from expanding remarkably,leaving less chances of the voids remaining in the package.

Second Embodiment

Referring to FIGS. 3 and 4(a)-4(d), a second embodiment of the presentinvention will be described. As shown in FIG. 3, the transfer moldingapparatus according to the second embodiment comprises a top-half mold16 a fixed to a top platen 26 a; a bottom-half mold 16 b fixed to abottom platen 26 b; heaters 18 for heating the top-half and thebottom-half molds 16 a, 16 b to a predetermined temperature; a transferpot 10, for accepting a tablet of a thermosetting resin, an epoxy resinfor example, formed by the top-half and the bottom-half molds 16 a and16 b; a plunger 12 for extruding the resin 28 melted in the transfer pot10; a suction pump 24 for reducing the pressure in the chamber 30,having the top-half and the bottom-half molds 16 a, 16 b installedtherein, thereby placing the cavities 20 at reduced pressure; and apressure controller 42 for controlling the drive of the suction pump 24according to the amount of movement of the plunger 12.

When the top-half mold 16 a and the bottom-half mold 16 b are closed,two runners (distribution paths) 22 for guiding the resin into thecavities 20 through gates 23, which are open to the cavities 20 areformed.

An air-vent slot 25 is formed on the side of each cavity 20 that isopposite the side open to the gate 23. When the chamber 30 is placed atreduced pressure by using a suction pump 24, the air in the cavities isextracted through the air-vent slots 25, so that the cavities 20 arealso placed at reduced pressure.

The pressure controller 42 is connected to a timer 42 a that counts theelapsed time from the start of plunger movement. The timer 42 a, when ithas counted the time until the cavity 20 is supplied with a specifiedamount of resin, outputs a detection signal to the pressure controller42. In response, the pressure controller 42 causes the suction pump 24to operate to reduce the pressure in the chamber 30. When the timer 42 ahas counted the time until the supply of resin 28 into the cavity 20 ais finished, the pressure controller 42 causes the suction pump 24 tostop. On the other hand, the chamber 30 is returned to normal pressure.

Referring to FIGS. 4(a)-4(d), description will be made of a method ofmanufacturing semiconductor devices on the transfer molding apparatusconstructed as described. FIGS. 4(a)-4(d) show the principal parts onlyfor convenience of explanation, and depicts the chamber 30 with analternate long and short dash line in a conceptual diagram.

After a semiconductor-element-mounted lead frame (not shown) is set inthe bottom-half mold 16 b, a resin tablet is charged in the transfer pot10, and by lowering the top platen 26 a, the top-half mold 16 a and thebottom-half mold 16 b are closed as shown in FIG. 4(a). At this point intime, the semiconductor element, not shown, has been placed almost inthe center of the cavity 20.

While the resin tablet charged in the transfer pot 10 is being melted byheating it to 160° to 190° C. by the heaters 18, the resin is extrudedfrom the transfer pot 10 by raising the plunger 12. By this operation,the molten resin 28 is introduced into the runner 22.

The timer 42 a starts counting time from the start of plunger movement,and as shown in FIG. 4(b), when the leading end of the plunger 12 hasmoved from position A to position B and the timer 42 a counts to time t1that indicates a specified amount of resin 28 has been supplied from therunner 22 into the cavity 20, the timer 42 a outputs a detection signalto the pressure controller 42. On receiving a detection signal from thetimer 42 a, the pressure controller 42 sends a drive start signal to thesuction pump 24. In response to the drive start signal, the suction pump24 starts to extract the air from the chamber 30, thus reducing thepressure in the chamber 30 to about 30 to 99 Pa.

In other words, when the timer has counted the previously calculatedtime t1 till each cavity 20 is supplied with a specified amount of resin28, the suction pump 24 gradually reduces the pressure in the cavity 20.For this reason, even if the resin 28 has been compressed at the gateposition 23 and the pressurized resin is injected into the cavity, therelative pressure difference between the pressure acting on the airbubbles in the resin 28 and the pressure in the cavity 20 is limited toa small degree. Therefore, the air bubbles entrapped in the resin can beprevented from expanding remarkably.

Timing for reducing the pressure in the chamber 30 by using the suctionpump 24 may be, for example, when the resin decreases in viscosity andstarts to harden (in this case, as shown in FIG. 4(c), when the resin 28has been injected up to one half of the cavity 20). In other words, thetiming for chamber pressure reduction may be when the timer 42 a hascounted time t2.

As described above, if the pressure in the chamber 30 is decreased afterthe resin has decreased in viscosity and has started to harden, the airbubbles in the resin are less liable to expand.

As shown in FIG. 4(d), when the cavity 20 is completely filled withresin 28, in other words, when the timer 42 a has counted time t3corresponding to the complete filling, the timer 42 a outputs adetection signal to the pressure controller 42. When receiving thedetection signal from the timer 42 a, the pressure controller 42transmits a drive stop signal to the suction pump 24 to stop itsoperation. On the other hand, the chamber 30 is brought back to normalpressure.

After the resin 28 has been sufficiently cured, the top platen 26 a (seeFIG. 3) is raised, and the semiconductor device with a lead frame in apackage of resin 28 that hardened around the semiconductor element isejected. Subsequently, the excess resin is removed, the package iswhittled down to shape, the frame portion of the lead frame is trimmed,and the outer leads are formed. Thus, a semiconductor device isobtained.

As has been described, in the second embodiment, when the timer 42 adetects the time when a specified amount of resin 28 has been suppliedto the cavity 20, the pressure controller 42 causes the suction pump 24to operate to reduce the pressure in the cavity 20. Therefore, therelative pressure difference between the pressure acting on the airbubbles in the resin 28 and the pressure in the cavity 20 can be limitedto a small degree. For this reason, even when the specified amount ofresin 28 has been supplied to the cavity 20, the air bubbles in theresin 28 can be prevented from expanding greatly, which makes itpossible to eliminate chances of voids remaining in the package.

Furthermore, even when the pressure in the chamber 30 is reduced afterthe resin 28 being injected into the cavity 20 has decreased inviscosity and has started to be cured, the air bubbles in the resin 28can be prevented from expanding greatly during filling.

Third Embodiment

A third embodiment of the present invention will be described withreference to FIGS. 5 and 6(a)-6(d). In the transfer molding apparatusaccording to the third embodiment, two pairs of first and secondcavities 20 a, 20 b, each pair being interconnected through a secondrunner 22 b, are formed by the top-half mold 16 a and the bottom-halfmold 16 b.

When the top-half mold 16 a and the bottom-half mold 16 b are closed, atransfer pot 10, a first runner 22 a communicating with the transfer pot10, a first cavity 20 a for accepting resin 28 from the first runner 22a through a first gate 23 a, a second runner 22 b communicating with thefirst cavity 20 a, and a second cavity 20 b for accepting resin 28 fromthe second runner 22 b through a second gate 23 b are formed on eitherside of the transfer pot 10 as shown in FIG. 5.

An air-vent slot 25 is formed on one side of each second cavity 20 bthat is opposite the side where there is the second gate 23 b. When thechamber 30 is placed at reduced pressure by extracting air by a suctionpump 24, the air is sucked out from the first and second cavities 20 a,20 b through the air-vent slots 25, so that the cavities 20 are placedat reduced pressure.

The pressure controller 40 drives the suction pump 24 to reduce thepressure in the chamber 30 when the position sensor 14 detects that theplunger 12 is at the position indicating that each cavity has beensupplied with a specified amount of resin. When the position sensor 14detects that the plunger 12 is at the position indicating that the firstcavity 20 a has been filled with resin 28 and also when the sensor 14detects that the plunger 12 is at the position indicating that thesecond cavity 20 b has been filled with resin 28, the pressurecontroller 40 causes the suction pump 24 to stop. On the other hand, thechamber 30 is brought back to normal pressure. Note that the otherfeatures of the third embodiment are the same as in the firstembodiment, and therefore their descriptions are omitted.

Referring to FIGS. 6(a)-6(d), description will be made of a method formanufacturing semiconductor devices on the transfer molding apparatusconstructed as described. FIGS. 6(a)-6(d) show only the principal partsfor convenience of explanation. Semiconductor-device-mounted lead frames(not shown) are set in the bottom-half mold 16 b, then a resin tablet isloaded in the transfer pot 10, and by lowering the top platen 26 a, thetop-half mold 16 a and the bottom-half mold 16 b are closed. At thistime, the semiconductor devices, not shown, have been placed almost inthe center of the first and the second cavities 20 a, 20 b.

While the resin tablet charged in the transfer pot 10 is being melted byheating it to 160° to 190° C. by the heaters 18, the resin is extrudedfrom the transfer pot 10 by raising the plunger 12. By this operation,the molten resin 28 is introduced into the first runners 22 a.

The position sensor 14 detects the position of the plunger 12 from thestart of its movement. As shown in FIG. 6(a), the position sensor 14outputs a detection signal to the pressure controller 40 when theposition sensor 14 detects that the leading end of the plunger 12 hasreached the position A, which indicates that a specified amount of resinhas been supplied from the first runner 22 a into the first cavity 20 a.

On receiving a detection signal from the position sensor 14, thepressure controller 40 transmits a drive start signal to the suctionpump 24. In response to the drive start signal, the suction pump 24starts to extract the air from the chamber 30, and gradually reduces thepressure in the chamber 30 to about 30 to 90 Pa.

Therefore, even if the resin 28 has been compressed at the first gateposition 23 a and the pressurized resin 28 is injected into the firstcavity 20 a, because the first cavity 20 a is gradually changed fromnormal pressure to reduced pressure, the relative pressure differencebetween the pressure applied to the air bubbles in the resin 28 and thepressure in the first cavity 20 a can be limited to a small degree, sothat the air bubbles entrapped in the resin can be prevented fromexpanding greatly.

Timing for reducing the pressure in the chamber 30 by using the suctionpump 24 may be when the resin decreases in viscosity and starts toharden, for example (in this case, when the resin 28 has been suppliedto about one half of the first cavity 20 a as shown in FIG. 6(b)). Inother words, the timing for chamber pressure reduction may be when theleading end of the plunger 12 has reached the position B.

As described above, if the pressure in the chamber 30 is decreased afterthe viscosity of the resin has decreased, because the resin has alreadystarted to harden, the air bubbles are less liable to expand in theresin supplied in the first cavity 20 a.

Subsequent to as shown in FIG. 6(b), when the cavity 20 a has beenfilled with the resin 28 once the plunger 12 moves past the position B,the position sensor 14 outputs a detection signal to the pressurecontroller 40. On receiving the detection signal from the positionsensor 14, the pressure controller 40 transmits a drive stop signal tothe suction pump 24. By this drive stop signal, the suction pump 24 isstopped and the chamber 30 is brought back to normal pressure.

When a specified amount of resin 28 has been supplied from the secondrunner 22 b to the second cavity 20 b, the position sensor 14 detectsthat the plunger 12 has reached the position C, as shown in FIG. 6(c).When the position sensor 14 detects that the leading end of the plunger12 arrived at the position C, the position sensor 14 outputs a detectionsignal to the pressure controller 40.

When receiving the detection signal from the position sensor 14, thepressure controller 40 transmits a drive start signal to the suctionpump 24, and the suction pump 24 starts to extract the air from thechamber 30 until the chamber 30 is reduced in pressure to about 30 to 90Pa.

Therefore, even if the resin 28 is compressed at the position of thegate 23 b and the pressurized resin 28 is injected into the secondcavity 23 b, because the second cavity 20 b is gradually changed fromnormal pressure to reduced pressure, the relative pressure differencebetween the pressure applied to the air bubbles in the resin 28 and thepressure in the second cavity 20 b can be limited to a small degree.Thus, the air bubbles entrapped in the resin can be prevented fromexpanding greatly.

Timing for reducing the pressure in the chamber 30 by using the suctionpump 24 may be when the resin decreases in viscosity and starts toharden (in this case, when the resin 28 has been injected to about onehalf of the cavity 20 b).

When the pressure in the chamber 30 is reduced after the viscosity ofthe resin in the second cavity 20 b has decreased as described above,because the resin has started to harden, the air bubbles in the secondcavity 20 b are less liable to expand.

Subsequently, when the leading end of the plunger 12 has moved to theposition D as shown in FIG. 6(d), which indicates that the second cavity20 b has been filled completely with the resin 28, the position sensor14 outputs a detection, signal to the pressure controller 40. Inresponse to the detection signal, the pressure controller 40 sends adrive stop signal to the suction pump 24. By the drive stop signal, thesuction pump 24 is stopped. On the other hand, the chamber 30 is broughtback to normal pressure. At the same time, the plunger movement is alsostopped, and the resin in the cavities 20 a and 20 b is cured.

After the resin 28 has been completely cured, the top platen 26 a (seeFIG. 5) is raised, a semiconductor device with a lead frame is ejectedwhich is encapsulated in the resin package that has been cured aroundthe semiconductor element. Subsequently, the excess resin is removed,the package is whittled to shape, the lead frame is trimmed, and theouter leads are formed. Thus, a semiconductor device is produced.

As described, according the third embodiment, when a specified amount ofresin is successively injected into the first and second cavities 20 a,20 b serially interconnected by the second runner 22 b, the pressurecontroller 40 causes the suction pump to operate to adjust the pressureof the cavities. Therefore, there is provided an advantage that aplurality of semiconductor devices are formed simultaneously in additionto the advantage described with reference to the first embodiment.

The shape of the mold is not limited to the one shown in FIGS. 5 and6(a)-6(d), but may be a type for producing a package with multiplegates, such as formed in matrix. In this case, by detection of theposition of the plunger 12 by the position sensor 14, it is possible toadjust the pressure of the cavities in a predetermined timing pattern,so that products without voids can be produced.

According to the third embodiment that has been described, the pressurecontroller 40 controls the suction pump according to the position of theplunger 12 detected by the position sensor 14. It is also possible toarrange for the pressure controller 40 to control the suction pumpaccording to time counted by the timer 42 a shown in FIGS. 4(a)-4(d).

More specifically, the pressure controller 40 drives the suction pump 24to reduce the pressure in the chamber 30 when the timer 42 a has countedtime until a specified amount of resin 28 has been injected into thefirst cavity 20 a, and when the timer 42 a has counted time until aspecified amount of resin has been injected into the second cavity 20 b.In this case, the pressure controller 40 causes the suction pump 24 tostop when the timer 42 a has counted time when the first cavity 20 a hasbeen completely filled with the resin 28 and time when the second cavity20 b has been completely filled with the resin 28.

In all the embodiments described above, the transfer molding apparatushas included one transfer pot for convenience of explanation. However,the present invention can be applied to transfer molding apparatuseshaving a plurality of transfer pots. Similarly, in all the embodimentsdescribed above, for convenience of explanation, the transfer moldingapparatus has included two runners communicating with the transfer pot,but the present invention can be applied to transfer molding apparatusesincluding one or more than three runners communicating with the transferpot.

As has been described, according to the present invention, there isprovided a transfer molding apparatus which prevents the expansion ofair bubbles in the resin resulting from a relative pressure differencebetween the pressure in the resin and the pressure in the cavity andthereby prevents the voids from remaining the package.

According to the method of manufacturing semiconductor devices with lesschances of voids remaining in the package.

1: A method of manufacturing a semiconductor device, comprising:arranging a semiconductor element in a cavity; introducing a specifiedamount of resin into the cavity; reducing a pressure in the cavity whenthe specified amount of resin has been supplied to the cavity; andfilling the cavity with the resin so that the semiconductor element iscovered by the resin. 2: The method of manufacturing a semiconductordevice of claim 1, wherein the specified amount of resin is an amount ofresin that fills about one half of the cavity. 3: The method ofmanufacturing a semiconductor device of claim 1, wherein the specifiedamount of resin is an amount of resin that is supplied to the cavitywithout hardening. 4: A method of manufacturing semiconductor devicepackages comprising: providing a transfer molding apparatus including atop-half mold and a bottom-half mold that forms a cavity as a moldingspace for a package, a transfer pot as a resin loading space, and aplunger that communicates with the transfer pot to force resin out ofthe pot and into the cavity; placing a semiconductor element between thetop-half mold and the bottom-half mold within the cavity; introducingresin into the cavity using the plunger; and reducing a pressure in thecavity using a suction pump to extract air from the cavity when aspecified amount of resin has been introduced to the cavity, to form asemiconductor device package. 5: The method of manufacturingsemiconductor device packages of claim 4, wherein the specified amountof resin is an amount of resin that fills about one half of the cavity.6: The method of manufacturing semiconductor device packages of claim 4,further comprising detecting a position of the plunger using a positionsensor, to determine when the specified amount of resin has beenintroduced to the cavity. 7: The method for manufacturing semiconductordevice packages of claim 4, further comprising detecting an amount oftime the plunger is driven using a timer, to determine when thespecified amount of resin has been introduced to the cavity. 8: Themethod of manufacturing semiconductor device packages of claim 4,wherein the specified amount of resin is an amount of resin that issupplied to the cavity without hardening. 9: A method of manufacturing asemiconductor device, comprising: placing a semiconductor elementbetween a top-half mold and a bottom-half mold; introducing resin into acavity formed by the top-half mold and the bottom-half mold using aplunger; determining an amount of time the plunger is driven using atimer; and reducing a pressure in the cavity by extracting air from thecavity using a suction pump, according to the amount of time the plungeris driven. 10: The method of manufacturing a semiconductor device ofclaim 9, wherein said reducing a pressure in the cavity begins once theplunger is driven an amount of time necessary to introduce an amount ofresin that fills about one half of the cavity. 11: The method ofmanufacturing a semiconductor device of claim 9, wherein said reducing apressure in the cavity begins once the plunger is driven an amount oftime necessary for the resin that is introduced into the cavity to beginhardening.